U.S. patent application number 16/983450 was filed with the patent office on 2020-11-19 for dynamic overdrive for liquid crystal displays.
The applicant listed for this patent is Synaptics Incorporated. Invention is credited to Stephen L. MOREIN.
Application Number | 20200365109 16/983450 |
Document ID | / |
Family ID | 1000004991780 |
Filed Date | 2020-11-19 |
United States Patent
Application |
20200365109 |
Kind Code |
A1 |
MOREIN; Stephen L. |
November 19, 2020 |
DYNAMIC OVERDRIVE FOR LIQUID CRYSTAL DISPLAYS
Abstract
A method and apparatus for overdriving pixel elements to a
desired voltage. A display device comprises a pixel array and
overdrive circuitry to determine a current pixel value for a first
pixel element of the pixel array and a target pixel value for the
first pixel element. The overdrive circuitry is further configured
to determine a first voltage to be applied to the first pixel
element to cause the first pixel element to transition from the
current pixel value to the target pixel value by a first instance
of time. The first voltage is determined based at least in part on
a position of the first pixel element in the pixel array. The
display device further comprises a data driver to apply the first
voltage to the first pixel element before the first instance of
time and a backlight to illuminate the pixel array at the first
instance of time.
Inventors: |
MOREIN; Stephen L.; (San
Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Synaptics Incorporated |
San Jose |
CA |
US |
|
|
Family ID: |
1000004991780 |
Appl. No.: |
16/983450 |
Filed: |
August 3, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16116862 |
Aug 29, 2018 |
10770023 |
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16983450 |
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62677564 |
May 29, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G 2310/08 20130101;
G09G 2320/0257 20130101; G09G 2320/064 20130101; G09G 3/3688
20130101; G09G 3/3406 20130101; G09G 2320/0666 20130101; G09G
3/3696 20130101; G09G 3/3677 20130101; G09G 2320/0252 20130101 |
International
Class: |
G09G 3/36 20060101
G09G003/36; G09G 3/34 20060101 G09G003/34 |
Claims
1. A method of updating pixel values of a pixel array, comprising:
determining a current pixel value and a target pixel value for a
first pixel element disposed in a first row of a plurality of rows
of the pixel array; determining a target voltage which causes the
first pixel element to settle at the target pixel value;
determining a first amount of overdrive voltage to be applied to
the first pixel element based at least in part on a display period
associated with the pixel array and an order in which voltages are
applied to the plurality of rows during a pixel adjustment period
preceding the display period, the overdrive voltage being greater
than the target voltage; applying the first amount of overdrive
voltage to the first pixel element during the pixel adjustment
period; and activating one or more light sources to illuminate the
pixel array during the display period.
2. The method of claim 1, wherein the first amount of overdrive
voltage is determined to cause the first pixel element to
transition from the current pixel value to the target pixel value
by the start of the display period.
3. The method of claim 1, further comprising: determining a current
pixel value and a target pixel value for a second pixel element
disposed in a second row of the plurality of rows, wherein a change
in pixel value from the current pixel value to the target pixel
value of the second pixel element is equal to a change in pixel
value from the current pixel value to the target pixel value of the
first pixel element; and determining a second amount of overdrive
voltage to be applied to the second pixel element based at least in
part on the display period and the order in which voltages are
applied to the plurality of rows of the pixel array during the
pixel adjustment period, the second amount of overdrive voltage
being different than the first amount.
4. The method of claim 3, wherein voltages are applied to the first
row of the pixel array earlier in the pixel adjustment period than
to the second row and the first amount of overdrive voltage is less
than the second amount.
5. The method of claim 3, wherein voltages are applied to the first
row of the pixel array later in the pixel adjustment period than to
the second row and the first amount of overdrive voltage is greater
than the second amount.
6. The method of claim 1, wherein the first amount of overdrive
voltage is determined based at least in part on a plurality of
lookup tables (LUTs), each of the plurality of LUTs indicating a
plurality of overdrive voltages for pixel elements in a respective
row of the plurality of rows.
7. The method of claim 6, wherein the determining of the first
amount of overdrive voltage further comprises: selecting a first
LUT of the plurality of LUTs associated with one of the plurality
of rows below the first row; selecting a second LUT of the
plurality LUTs associated with one of the plurality of rows above
of the first row; and performing a linear interpolation of the
first LUT and the second LUT to determine the first amount of
overdrive voltage.
8. The method of claim 7, wherein the determining of the first
amount of overdrive voltage further comprises: generating an
interpolated LUT based on the linear interpolation of the first and
second LUTs; selecting at least two rows of the interpolated LUT
based on the current pixel value; selecting at least two columns of
the interpolated LUT based on the target pixel value; and
performing a bilinear interpolation of the selected rows and
columns of the interpolated LUT to determine the first amount of
overdrive voltage.
9. The method of claim 7, wherein the first and second LUTs are
selected based at least in part on a temperature of the pixel
array.
10. The method of claim 1, wherein the determining of the first
amount of overdrive voltage comprises: determining a maximum amount
of overdrive voltage applicable to the first pixel element based on
a voltage range of a data driver configured to supply the overdrive
voltage; determining whether a line number associated with the
first row is greater than or equal to a threshold line number of
the pixel array; and selecting the first amount of overdrive
voltage to be equal to the maximum amount responsive to determining
that the line number is greater than or equal to the threshold line
number.
11. A display device, comprising: one or more processors; and a
memory storing instructions that, when executed by the one or more
processors, cause the display device to: determine a current pixel
value and a target pixel value for a first pixel element disposed
in a first row of a plurality of rows of the pixel array; determine
a target voltage which causes the first pixel element to settle at
the target pixel value; and determine a first amount of overdrive
voltage to be applied to the first pixel element based at least in
part on a display period associated with the pixel array and an
order in which voltages are applied to the plurality of rows during
a pixel adjustment period preceding the display period, the
overdrive voltage being greater than the target voltage; apply the
first amount of overdrive voltage to the first pixel element during
the pixel adjustment period; and activate one or more light sources
to illuminate the pixel array during the display period.
12. The display device of claim 11, wherein the first amount of
overdrive voltage is determined to cause the first pixel element to
transition from the current pixel value to the target pixel value
by the start of the display period.
13. The display device of claim 11, wherein execution of the
instructions further causes the display device to: determine a
current pixel value and a target pixel value for a second pixel
element disposed in a second row of the plurality of rows, wherein
a change in pixel value from the current pixel value to the target
pixel value of the second pixel element is equal to a change in
pixel value from the current pixel value to the target pixel value
of the first pixel element; and determine a second amount of
overdrive voltage to be applied to the second pixel element based
at least in part on the display period and the order in which
voltages are applied to the plurality of rows of the pixel array
during the pixel adjustment period, the second amount of overdrive
voltage being different than the first amount.
14. The display device of claim 13, wherein voltages are applied to
the first row of the pixel array earlier in the pixel adjustment
period than to the second row and the first amount of overdrive
voltage is less than the second amount.
15. The display device of claim 13, wherein voltages are applied to
the first row of the pixel array later in the pixel adjustment
period than to the second row and the first amount of overdrive
voltage is greater than the second amount.
16. The display device of claim 11, wherein the first amount of
overdrive voltage is determined based at least in part on a
plurality of lookup tables (LUTs), each of the plurality of LUTs
indicating a plurality of overdrive voltages for pixel elements in
a respective row of the plurality of rows.
17. The display device of claim 16, wherein execution of the
instructions for determining the first amount of overdrive voltage
further causes the display device to: select a first LUT, of the
plurality of LUTs, associated with one of the plurality of rows
below the first row; select a second LUT, of the plurality LUTs,
associated with one of the plurality of rows above the first row;
and perform a linear interpolation of the first LUT and the second
LUT to determine the first amount of overdrive voltage.
18. The display device of claim 17, wherein execution of the
instructions for determining the first amount of overdrive voltage
further causes the display device to: generate an interpolated LUT
based on the linear interpolation of the first and second LUTs;
select at least two rows of the interpolated LUT based on the
current pixel value; select at least two columns of the
interpolated LUT based on the target pixel value; and perform a
bilinear interpolation of the selected rows and columns of the
interpolated LUT to determine the first amount of overdrive
voltage.
19. The display device of claim 17, wherein the first and second
LUTs are selected based at least in part on a temperature of the
pixel array.
20. The display device of claim 11, wherein execution of the
instructions for determining the first amount of overdrive voltage
causes the display device to: determine a maximum amount of
overdrive voltage applicable to the first pixel element based on a
voltage range of a data driver configured to supply the overdrive
voltage; determine whether a line number associated with the first
row is greater than or equal to a threshold line number of the
pixel array; and select the first amount of overdrive voltage to be
equal to the maximum amount responsive to determining that the line
number is greater than or equal to the threshold line number.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 16/116,862, filed Aug. 29, 2018, entitled "DYNAMIC OVERDRIVE
FOR LIQUID CRYSTAL DISPLAYS," which claims priority and benefit
under 35 USC .sctn. 119(e) to U.S. Provisional Patent Application
No. 62/677,564, filed on May 29, 2018, the entireties of which are
incorporated by reference herein.
TECHNICAL FIELD
[0002] The present embodiments relate generally to liquid-crystal
displays (LCDs), and specifically to dynamic overdrive techniques
for LCD devices.
BACKGROUND OF RELATED ART
[0003] Head-mounted display (HMD) devices are configured to be worn
on, or otherwise affixed to, a user's head. An HMD device may
comprise one or more displays positioned in front of one, or both,
of the user's eyes. The HMD may display images (e.g., still images,
sequences of images, and/or videos) from an image source overlaid
with information and/or images from the user's surrounding
environment (e.g., as captured by a camera), for example, to
immerse the user in a virtual world. HMD devices have applications
in medical, military, gaming, aviation, engineering, and various
other professional and/or entertainment industries.
[0004] HMD devices may use liquid-crystal display (LCD)
technologies in their displays. An LCD display panel may be formed
from an array of pixel elements (e.g., liquid crystal cells)
arranged in rows and columns. Each row of pixel elements is coupled
to a respective gate line, and each column of pixel elements is
coupled to a respective data (or source) line. A pixel element may
be accessed (e.g., updated with new pixel data) by driving a
relatively high voltage on a gate line to "select" or activate a
corresponding row of pixel elements, and driving another voltage on
a corresponding data line to apply the update to the selected pixel
element. The voltage level of the data line may depend on the
desired color and/or intensity of the target pixel value. Thus, LCD
display panels may be updated by successively "scanning" the rows
of pixel elements (e.g., one row at a time), until each row of the
pixel array has been updated.
[0005] The voltage applied on the data line changes the color
and/or brightness of the pixel element by changing the physical
state of (e.g., rotating) the particular pixel element. Thus, each
pixel element may require time to settle into the new state or
position. The settling time of a particular pixel element may
depend on the degree of change in color and/or brightness. For
example, transitioning from a maximum brightness setting (e.g., a
"white" pixel) to a minimum brightness setting (e.g., a "black"
pixel) may require greater settling time than transitioning from an
intermediate brightness setting to another intermediate brightness
setting (e.g., from one shade of "gray" to a different shade of
"gray"). The delay in pixel transition may cause ghosting and/or
other visual artifacts to appear on the display when the settling
time of the pixel elements is slower than the time between
successive frame updates.
[0006] LCD overdrive is a technique for accelerating pixel
transitions when updating an LCD display. Specifically, a pixel
element is driven to a higher voltage than the target voltage
associated with the desired color and/or brightness level. The
higher voltage causes the liquid crystal to rotate faster, and thus
reach the target brightness in less time. On fixed LCD displays
(e.g., televisions, monitors, mobile phones, etc.), an object is
often illuminated by the same pixel elements for the duration of
multiple frames. Thus, the amount of overdrive applied to the pixel
elements of a fixed LCD display can be approximate since the user
may be unable to detect errors in the corresponding pixel color
and/or brightness when such errors last only a single frame.
However, on HMD devices, and particularly in virtual reality (VR)
applications, an object viewed on the display may be illuminated by
different pixels as the user's head and/or eyes move. Therefore,
the amount of overdrive applied to each pixel element of an HMD
display should be much more precise to preserve the user's sense of
immersion in the virtual environment.
SUMMARY
[0007] This Summary is provided to introduce in a simplified form a
selection of concepts that are further described below in the
Detailed Description. This Summary is not intended to identify key
features or essential features of the claims subject matter, nor is
it intended to limit the scope of the claimed subject matter.
[0008] A method and apparatus for overdriving pixel elements to a
desired voltage. A display device a pixel array and overdrive
circuitry to determine a current pixel value for a first pixel
element of the pixel array and a target pixel value for the first
pixel element. The overdrive circuitry is further configured to
determine a first voltage to be applied to the first pixel element
to cause the first pixel element to transition from the current
pixel value to the target pixel value by a first instance of time.
The first voltage is determined based at least in part on a
position of the first pixel element in the pixel array. The display
device further comprises a data driver to apply the first voltage
to the first pixel element before the first instance of time and a
backlight to illuminate the pixel array at the first instance of
time.
[0009] The position of the first pixel element may correspond to a
row position in the pixel array. In some embodiments, the first
voltage may correspond to a target voltage when the row position is
located below a threshold line number of the pixel array, wherein
the target voltage causes the first pixel element to settle at the
target pixel value. In some other embodiments, the first voltage
may correspond to an overdrive voltage when the row position is
located above the threshold line number of the pixel array, wherein
the overdrive voltage is different than the target voltage.
[0010] In some embodiments, the overdrive circuitry may comprise a
lookup table (LUT) repository configured to store a plurality of
LUTs and an overdrive voltage generator to determine the first
voltage based at least in part on the plurality of LUTs. In some
aspects, each of the LUTs may indicate a plurality of overdrive
voltages for pixel elements in a corresponding row of the pixel
array.
[0011] In some embodiments, the overdrive voltage generator may
select first and second LUTs of the plurality of LUTs based at
least in part on the row position of the first pixel element. For
example, the first LUT may be associated with a row of the pixel
array below the row position of the first pixel element and the
second LUT may be associated with a row of the pixel array above
the row position of the first pixel element. The overdrive voltage
generator may further determine the first voltage based at least in
part on a linear interpolation of the first LUT and the second LUT.
In some aspects, the overdrive voltage generator may select the
first and second LUTs based at least in part on a temperature of
the display.
[0012] In some embodiments, the overdrive voltage generator may
comprise an LUT generator to generate an interpolated LUT based on
the linear interpolation of the first and second LUTs. The
overdrive voltage generator may further include an overdrive
voltage interpolator configured to select at least two rows of the
interpolated LUT based on the current pixel value and select at
least two columns of the interpolated LUT based on the target pixel
value. The overdrive voltage interpolator is further configured to
determine the first voltage based on a bilinear interpolation of
the selected rows and columns of the interpolated LUT.
[0013] In some embodiments, the overdrive circuitry may be further
configured to determine a second voltage to be applied to a second
pixel element of the pixel array to cause the second pixel element
to transition from the current pixel value to the target pixel
value by the first instance of time. More specifically, the second
voltage may be different than the first voltage. In some aspects,
the data driver may be further configured to apply the second
voltage to the second pixel element before the first instance of
time. In some aspects, the first pixel element may be located in a
different row of the pixel array than the first pixel element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present embodiments are illustrated by way of example
and are not intended to be limited by the figures of the
accompanying drawings.
[0015] FIG. 1 shows an example display system within which the
present embodiments may be implemented.
[0016] FIG. 2 shows a block diagram of a display device with
overdrive circuitry, in accordance with some embodiments.
[0017] FIG. 3 shows a timing diagram depicting an example timing of
pixel updates in a display device, in accordance with some
embodiments.
[0018] FIGS. 4A and 4B show timing diagrams depicting example
implementations of progressive overdrive, in accordance with some
embodiments.
[0019] FIGS. 5A and 5B show block diagrams of a progressive
overdrive controller, in accordance with some embodiments.
[0020] FIG. 6 shows an example pair of look-up tables (LUTs) that
can be used to generate progressive overdrive voltages, in
accordance with some embodiments.
[0021] FIG. 7 shows a block diagram of a progressive overdrive
controller, in accordance with some other embodiments.
[0022] FIG. 8 is an illustrative flowchart depicting an example
operation for driving a pixel element of a display to a target
pixel value.
[0023] FIG. 9 is an illustrative flowchart depicting an example
operation for selectively applying overdrive voltages to the pixel
elements of a pixel array.
[0024] FIG. 10 is an illustrative flowchart depicting an example
operation for determining an overdrive voltage to be used to drive
a pixel element to a target pixel value.
DETAILED DESCRIPTION
[0025] In the following description, numerous specific details are
set forth such as examples of specific components, circuits, and
processes to provide a thorough understanding of the present
disclosure. The term "coupled" as used herein means connected
directly to or connected through one or more intervening components
or circuits. The terms "electronic system" and "electronic device"
may be used interchangeably to refer to any system capable of
electronically processing information. Also, in the following
description and for purposes of explanation, specific nomenclature
is set forth to provide a thorough understanding of the aspects of
the disclosure. However, it will be apparent to one skilled in the
art that these specific details may not be required to practice the
example embodiments. In other instances, well-known circuits and
devices are shown in block diagram form to avoid obscuring the
present disclosure. Some portions of the detailed descriptions
which follow are presented in terms of procedures, logic blocks,
processing and other symbolic representations of operations on data
bits within a computer memory.
[0026] These descriptions and representations are the means used by
those skilled in the data processing arts to most effectively
convey the substance of their work to others skilled in the art. In
the present disclosure, a procedure, logic block, process, or the
like, is conceived to be a self-consistent sequence of steps or
instructions leading to a desired result. The steps are those
requiring physical manipulations of physical quantities. Usually,
although not necessarily, these quantities take the form of
electrical or magnetic signals capable of being stored,
transferred, combined, compared, and otherwise manipulated in a
computer system. It should be borne in mind, however, that all of
these and similar terms are to be associated with the appropriate
physical quantities and are merely convenient labels applied to
these quantities.
[0027] Unless specifically stated otherwise as apparent from the
following discussions, it is appreciated that throughout the
present application, discussions utilizing the terms such as
"accessing," "receiving," "sending," "using," "selecting,"
"determining," "normalizing," "multiplying," "averaging,"
"monitoring," "comparing," "applying," "updating," "measuring,"
"deriving" or the like, refer to the actions and processes of a
computer system, or similar electronic computing device, that
manipulates and transforms data represented as physical
(electronic) quantities within the computer system's registers and
memories into other data similarly represented as physical
quantities within the computer system memories or registers or
other such information storage, transmission or display
devices.
[0028] In the figures, a single block may be described as
performing a function or functions; however, in actual practice,
the function or functions performed by that block may be performed
in a single component or across multiple components, and/or may be
performed using hardware, using software, or using a combination of
hardware and software. To clearly illustrate this
interchangeability of hardware and software, various illustrative
components, blocks, modules, circuits, and steps have been
described below generally in terms of their functionality. Whether
such functionality is implemented as hardware or software depends
upon the particular application and design constraints imposed on
the overall system. Skilled artisans may implement the described
functionality in varying ways for each particular application, but
such implementation decisions should not be interpreted as causing
a departure from the scope of the present invention. Also, the
example input devices may include components other than those
shown, including well-known components such as a processor, memory
and the like.
[0029] The techniques described herein may be implemented in
hardware, software, firmware, or any combination thereof, unless
specifically described as being implemented in a specific manner.
Any features described as modules or components may also be
implemented together in an integrated logic device or separately as
discrete but interoperable logic devices. If implemented in
software, the techniques may be realized at least in part by a
non-transitory processor-readable storage medium comprising
instructions that, when executed, performs one or more of the
methods described above. The non-transitory processor-readable data
storage medium may form part of a computer program product, which
may include packaging materials.
[0030] The non-transitory processor-readable storage medium may
comprise random access memory (RAM) such as synchronous dynamic
random access memory (SDRAM), read only memory (ROM), non-volatile
random access memory (NVRAM), electrically erasable programmable
read-only memory (EEPROM), FLASH memory, other known storage media,
and the like. The techniques additionally, or alternatively, may be
realized at least in part by a processor-readable communication
medium that carries or communicates code in the form of
instructions or data structures and that can be accessed, read,
and/or executed by a computer or other processor.
[0031] The various illustrative logical blocks, modules, circuits
and instructions described in connection with the embodiments
disclosed herein may be executed by one or more processors. The
term "processor," as used herein may refer to any general purpose
processor, conventional processor, controller, microcontroller,
and/or state machine capable of executing scripts or instructions
of one or more software programs stored in memory. The term
"voltage source," as used herein may refer to a direct-current (DC)
voltage source, an alternating-current (AC) voltage source, or any
other means of creating an electrical potential (such as
ground).
[0032] FIG. 1 shows an example display system 100 within which the
present embodiments may be implemented. The display system 100
includes a host device 110 and a display device 120. The display
device 120 may be any device configured to display an image, or
sequence of images (e.g., video), to a user. In some embodiments,
the display device 120 may be a head-mounted display (HMD) device.
In some aspects, the host device 110 may be implemented as a
physical part of the display device 120. Alternatively, the host
device 110 may be coupled to (and communicate with) components of
the display device 120 using various wired and/or wireless
interconnection and communication technologies, such as buses and
networks. Example technologies may include Inter-Integrated Circuit
(1.sup.2C), Serial Peripheral Interface (SPI), PS/2, Universal
Serial bus (USB), Bluetooth.RTM., Infrared Data Association (IrDA),
and various radio frequency (RF) communication protocols defined by
the IEEE 802.11 standard.
[0033] The host device 110 receives image source data 101 from an
image source (not shown for simplicity) and renders the image
source data 101 for display (e.g., as display data 102) on the
display device 120. In some embodiments, the host device 110 may
include a rendering engine 112 configured to process the image
source data 101 according to one or more capabilities of the
display device 120. For example, in some aspects, the display
device 120 may display a dynamically-updated image to a user based
on the user's eye position. More specifically, the display device
120 may track the user's head and/or eye movements and may display
a portion of the image coinciding with a fixation point of the user
(e.g., foveal region) with higher resolution than other regions of
the image (e.g., the full-frame image). Thus, in some embodiments,
the rendering engine 112 may generate a high-resolution foveal
image to be overlaid in the foveal region of the full-frame image.
In some other embodiments, the rendering engine 112 may scale the
full-frame image for display (e.g., at a lower-resolution than the
foveal image) on the display device 120.
[0034] The display device 120 receives the display data 102 from
the host device 110 and displays a corresponding image to the user
based on the received display data 102. In some embodiments, the
display device 120 may include a display 122 and a backlight 124.
The display 122 may be a liquid-crystal display (LCD) panel formed
from an array of pixel elements (e.g., liquid crystal cells)
configured to allow varying amounts of light to pass from one
surface of the display panel to another (e.g., depending on a
voltage or electric field applied to each pixel element). For
example, the display device 120 may apply an appropriate voltage to
each of the pixel elements to render an image (which may include a
foveal image overlaid upon a full-frame image) on the display 122.
As described above, LCDs do not emit light and therefore rely on a
separate light source to illuminate the pixel elements so that the
image is viewable by the user.
[0035] The backlight 124 may be positioned adjacent the display 122
to illuminate the pixel elements from behind. The backlight 124 may
comprise one or more light sources including, but not limited to,
cold cathode fluorescent lamps (CCFLs), external electrode
fluorescent lamps (EEFLs), hot-cathode fluorescent lamps (HCFLs),
flat fluorescent lamps (FFLs), light-emitting diodes (LEDs), or any
combination thereof. In some aspects, the backlight 124 may include
an array of discrete light sources (such as LEDs) that can provide
different levels of illumination to different regions of the
display 122. In some embodiments, the display device 120 may
include an inverter (not shown for simplicity) that can dynamically
alter the intensity or brightness of the backlight 124, for
example, to enhance image quality and/or conserve power.
[0036] As described above, the color and/or brightness of each
pixel element may be adjusted by changing the voltage applied to
that pixel element. However, the degree of change in color and/or
brightness that can be achieved in a single frame transition or
update may be limited by the settling time of the pixel element.
For example, transitioning from a maximum brightness setting (e.g.,
a "white" pixel) to a minimum brightness setting (e.g., a "black"
pixel) may require greater settling time than transitioning from an
intermediate brightness setting to another intermediate brightness
setting (e.g., from one shade of "gray" to a different shade of
"gray"). If the pixel element is unable to achieve the desired
color and/or brightness between successive frame updates, artifacts
(such as ghosting) may appear in the displayed image.
[0037] LCD overdrive is a technique for increasing the speed of
pixel transitions when updating an LCD display. Specifically, a
pixel element is driven to a higher voltage than the target voltage
associated with the desired color and/or brightness level. The
higher voltage causes the liquid crystal in each pixel element to
rotate faster, and thus reach the target brightness in less time.
Thus, in some embodiments, the display system 100 may include
overdrive circuitry (not shown for simplicity) that can dynamically
adjust the amount of voltage to be applied to each pixel element in
the display 122 to reduce the occurrence of artifacts and/or
prevent them from interfering with the user's viewing
experience.
[0038] FIG. 2 shows a block diagram of a display device 200 with
overdrive circuitry, in accordance with some embodiments. The
display device 200 may be an example embodiment of the display 122
of the display device 120 of FIG. 1. More specifically, the display
device 200 may include a pixel array 210, a timing controller 220,
a display memory 230, and overdrive (OD) circuitry 240. In some
embodiments, the display device 200 may correspond to an LCD
display panel. Thus, the pixel array 210 may comprise a plurality
of liquid crystal pixel elements (not shown for simplicity). Each
row of pixel elements is coupled to a respective gate line (GL),
and each column of pixel elements is coupled to a respective data
line (DL). Accordingly, each pixel element in the array 210 is
positioned at an intersection of a gate line and a source line.
[0039] A data driver 212 is coupled to the pixel array 210 via the
data lines DL(1)-DL(N). In some aspects, the data driver 212 may be
configured to drive pixel data (e.g., in the form of a
corresponding voltage) to individual pixel elements, via the data
lines DL(1)-DL(N), to update a frame or image displayed by the
pixel array 210. For example, the voltage driven onto the data
lines DL(1)-DL(N) may alter the physical state (e.g., rotation) of
the pixel elements in the array 210 (e.g., where the pixel elements
are liquid crystals). Thus, the voltage applied to each pixel
element may directly affect the color and/or intensity of light
emitted by that pixel element. It is noted that each row of pixel
elements in the pixel array 210 is coupled to the same data lines
DL(1)-DL(N). Thus, the display device 200 may update the pixel
array 210 by successively scanning the rows of pixel elements.
[0040] A gate driver 214 is coupled to the pixel array 210 via the
gate lines GL(1)-GL(M). In some aspects, the gate driver 214 may be
configured to select which row of pixel elements is to receive the
pixel data driven by the data driver 212 at any given time. For
example, each pixel element in the array 210 may be coupled to one
of the data lines DL(1)-DL(N) and one of the gate lines GL(1)-GL(M)
via an access transistor (not shown for simplicity). The access
transistor may be an NMOS (or PMOS) transistor having a gate
terminal coupled to one of the gate lines GL(1)-GL(M), a drain (or
source) terminal coupled to one of the source lines DL(1)-DL(N),
and a source (or drain) terminal coupled to a corresponding pixel
element in the array 210. When one of the gate lines GL(1)-GL(M) is
driven with a sufficiently high voltage, the access transistors
coupled to the selected gate line turn on and allow current to flow
from the data lines DL(1)-DL(N) to the corresponding row of pixel
elements. Accordingly, the gate driver 214 may be configured to
select or activate each of the gate lines GL(1)-GL(M), in
succession, until each row of the pixel array 210 has been
updated.
[0041] The timing controller 220 is configured to control a timing
of the data driver 212 and the gate driver 214. For example, the
timing controller 220 may generate a first set of timing control
signals (D_CTRL) to control activation of the data lines
DL(1)-DL(N) by the data driver 212. The timing controller 220 may
also generate a second set of timing control signals (G_CTRL) to
control activation of the gate lines GL(1)-GL(M) by the gate driver
214. The timing controller 220 may generate the S_CTRL and G_CTRL
signals based on a reference clock signal generated by a signal
generator 222. For example, the signal generator 222 may be a
crystal oscillator. The timing controller 220 may drive the D_CTRL
and G_CTRL signals based by applying respective phase offsets to
the reference clock signal. More specifically, the timing of the
D_CTRL signals and G_CTRL signals may be synchronized such that the
gate driver 214 activates the correct gate line (e.g., coupled to
the row of pixel elements to be driven with pixel data) at the time
the data driver 212 drives the data lines DL(1)-DL(N) with the
pixel data intended for that row of pixel elements.
[0042] The display memory 230 may be configured to store or buffer
display data 203 to be displayed on the pixel array 210. The
display data 203 may include pixel values 204 (e.g., corresponding
to a color and/or intensity) for each pixel element in the array
210. For example, each pixel element may comprise a plurality of
subpixels including, but not limited to, red (R), green (G), and
blue (B) subpixels. In some aspects, the display data 203 may
indicate R, G, and B values for the subpixels of the image to be
displayed. The R, G, and B values may affect the color and
intensity (e.g., gray level) of each pixel element. For example,
each pixel value 204 may be an 8-bit value representing one of 256
possible grayscale levels. As described above, each pixel value 204
may be associated with a target voltage level. In other words, when
the target voltage is applied to a particular pixel element, the
color and/or brightness of the pixel element will eventually settle
to the desired pixel value. However, the settling time of the pixel
element may depend on the degree of change in pixel value. Thus, if
the change in pixel value exceeds a threshold amount, the target
voltage may be insufficient to drive the pixel element to the
desired pixel value within a given frame update period.
[0043] The overdrive circuitry 240 may determine an overdrive
voltage 205 to be applied to one or more pixel elements in the
array 210 based, at least in part, on the pixel values 204. More
specifically, for each pixel element of the array 210, the
overdrive circuitry 240 may compare the current pixel value (e.g.,
the pixel value from a previous frame update) to a target pixel
value (e.g., the pixel value for the next frame update) to
determine the amount of voltage to be applied to the pixel element
to effect the change in pixel value within a frame update period.
In some aspects, the overdrive circuitry 240 may compare the
current pixel value and target pixel value to corresponding values
in a lookup table (LUT) to determine the overdrive voltage 205 to
be applied to the pixel element to effect the desired change in
pixel value. In some instances, the overdrive voltage 205 may
exceed (e.g., may be higher or lower than) the target voltage.
However, the overdrive voltage 205 may be limited (e.g., capped) by
the voltage range of the data driver 212. Thus, a pixel element may
not exceed a threshold change in pixel value within any frame
update period.
[0044] As described above, individual rows of the pixel array 210
may be successively updated (e.g., one row at a time). However, the
image rendered on the pixel array 210 may not be viewable unless
the pixel elements are illuminated by a light source (such as the
backlight 124 of FIG. 1). In a fixed LCD display, the backlight may
provide continuous illumination to the pixel array (e.g., the
backlight is constantly on or at least pulse-width modulated to a
desired brightness level). Thus, any changes in pixel values may be
noticeable as soon as the updated voltages are applied to the pixel
elements. However, in virtual reality (VR) applications, an object
viewed on the display may be illuminated by different pixels as the
user's head and/or eyes move. Rapid changes in pixel values may
cause motion blur and/or other artifacts in the images rendered on
the LCD display, which may impair the virtual reality experience.
The display device may reduce or prevent motion blur by
periodically (rather than continuously) updating the display. For
example, the display device may flash the backlight at periodic
intervals so that rapid changes in pixel values in between such
intervals are suppressed (e.g., similar to the saccadic suppression
phenomenon in human visual perception).
[0045] With reference for example to the timing diagram 300 of FIG.
3, images may be periodically displayed by the pixel array 210
during successive frame update intervals. More specifically, each
frame update interval (e.g. from times t.sub.0-t.sub.3 and
t.sub.3-t.sub.6) may comprise a pixel adjustment period (e.g., from
times t.sub.0-t.sub.2 and t.sub.3-t.sub.5) followed by a display
period (e.g., from times t.sub.2-t.sub.3 and t.sub.5-t.sub.6).
During each pixel adjustment period, the pixel array 210 may be
driven with pixel updates (e.g., from times t.sub.0-t.sub.1 and
t.sub.3 to t.sub.4). The updated pixel elements are then
"displayed" (e.g. made viewable) to the user during the following
display period. For example, the image on the pixel array 210 may
be displayed to the user by activating a light source configured to
illuminate the pixel array 210 (such as the backlight 124 of FIG.
1).
[0046] During each pixel adjustment period, individual rows of the
pixel array 210 may be successively updated (e.g., in a cascaded
fashion). The curves 301 and 302 show example pixel update times
for each row of the pixel array 210 based on the line number
associated with that row. Thus, as shown in FIG. 3, rows associated
with higher line numbers (e.g., further down the cascade) are
updated later than rows associated with lower line numbers (e.g.,
towards the start of the cascade). However, because the pixel
elements are illuminated only during the display periods, any
changes in pixel value exhibited before or after the display period
will not be seen by the user. As a result, pixel elements
associated with higher line numbers (e.g., pixel elements that are
updated later) have less time to transition to their desired pixel
values than pixel elements associated with lower line numbers
(e.g., pixel elements that are updated earlier). For example, pixel
elements at the top of the array 210 may have the duration (T) of
the pixel adjustment period to reach their target pixel values. In
contrast, pixel elements in the middle of the array 210 may have a
significantly shorter duration (T-x) to reach their target pixel
values, and pixel elements at the bottom of the array 210 may have
an even shorter duration (T-2x) to reach their target pixel
values.
[0047] Aspects of the present disclosure recognize that, due to the
differences in transition times for the various rows of the pixel
array 210, different amounts of overdrive may be applied to
different rows of pixel elements. For example, pixel elements
associated with relatively low line numbers may require less
overdrive voltage (if any) to reach their target pixel values
before the next display period. However, pixel elements associated
with higher line numbers may require progressively more overdrive
voltage to reach their target pixel values before the next display
period. Thus, in some embodiments, the overdrive circuitry 240 may
progressively increase the amount of overdrive applied to the rows
of pixel elements based, at least in part, on their position (e.g.,
line number) in the array 210. More specifically, pixel elements
that are associated with higher line numbers (e.g. updated later
during the display update interval) are generally provided with
greater amounts of overdrive voltage than pixel elements that are
associated with lower line numbers (e.g., updated earlier during
the display update interval).
[0048] FIG. 4A shows a timing diagram 400A depicting an example
implementation of progressive overdrive, in accordance with some
embodiments. In some embodiments, the method of progressive
overdrive illustrated in FIG. 4A may be implemented by the
overdrive circuitry 240 of FIG. 2. The timing diagram 400A shows an
example frame update interval (e.g. from times t.sub.0-t.sub.2)
which may comprise a pixel adjustment period (e.g., from times
t.sub.0-t.sub.1) followed by a display period (e.g., from times
t.sub.1-t.sub.2). The curve 401 depicts example pixel update times
for each row of the pixel array 210 based on the line number
associated with that row.
[0049] In the example of FIG. 4A, the overdrive circuitry 240 may
generate progressive overdrive voltages for successive rows of
pixel elements between lines l.sub.0 to l.sub.p of the pixel array
210. More specifically, the amount of overdrive voltage may be
progressively increased for each successive row of pixel elements
from lines l.sub.0 to l.sub.p. For example, a pixel element coupled
to line l.sub.p may be driven to a higher voltage than a pixel
element coupled to line l.sub.0 to effect the same change in pixel
value (e.g., same change in grayscale level) before the start of
the display period. As described above, the amount of overdrive
that can be applied to the pixel elements may be limited by the
voltage range of the data driver 212. In the example of FIG. 4A,
the overdrive voltage may become saturated by the time the pixel
elements coupled to line l.sub.p are updated. Thus, the overdrive
circuitry 240 may apply maximum overdrive to the rows of pixel
elements between lines l.sub.p and l.sub.M of the pixel array 210.
In other words, if any of the pixel elements between lines l.sub.p
and l.sub.M are to be updated during the pixel adjustment period,
the overdrive circuitry 240 may apply the maximum overdrive voltage
to change the pixel values of such pixel elements.
[0050] Aspects of the present disclosure recognize that the need
for progressive overdrive may vary depending on the characteristics
of the LCD display (e.g., number of pixels, temperature, response
time, etc.). For example, an LCD display with fewer pixel elements
(or at least fewer lines of pixels) may require less time to update
the entire pixel array. Thus, the change in overdrive from one row
of pixel elements to another may be more gradual in a smaller pixel
array. Aspects of the present disclosure further recognize that, in
some embodiments, one or more rows of pixel elements may settle to
their target pixel values, before the next display period, without
the use of overdrive (e.g., by driving the pixel elements only up
to the target voltage).
[0051] FIG. 4B shows a timing diagram 400B depicting another
example implementation of progressive overdrive, in accordance with
some embodiments. In some embodiments, the method of progressive
overdrive illustrated in FIG. 4B may also be implemented by the
overdrive circuitry 240 of FIG. 2. The timing diagram 400B shows an
example frame update interval (e.g. from times t.sub.0-t.sub.2)
which may comprise a pixel adjustment period (e.g., from times
t.sub.0-t.sub.1) followed by a display period (e.g., from times
t.sub.1-t.sub.2). The curve 402 depicts example pixel update times
for each row of the pixel array 210 based on the line number (e.g.,
gate line) associated with that row.
[0052] In the example of FIG. 4B, the overdrive circuitry 240 may
not apply any overdrive to the rows of pixel elements between lines
l.sub.0 and l.sub.n of the pixel array 210. Rather, each pixel
element between lines l.sub.0 and l.sub.n may be driven to its
target voltage during the pixel adjustment period. The overdrive
circuitry 240 may generate progressive overdrive voltages for
successive rows of pixel elements between lines l.sub.n to l.sub.p
of the pixel array 210. As described above, the amount of overdrive
voltage may be progressively increased for each successive row of
pixel elements from lines l.sub.n to l.sub.p. In the example of
FIG. 4B, the overdrive voltage may become saturated by the time the
pixel elements coupled to line l.sub.p are updated. Thus, the
overdrive circuitry 240 may apply maximum overdrive to the rows of
pixel elements between lines l.sub.p and l.sub.M of the pixel array
210. In other words, if any of the pixel elements between lines
l.sub.p and l.sub.M are to be updated during the pixel adjustment
period, the overdrive circuitry 240 may apply the maximum overdrive
voltage to change the pixel values of such pixel elements.
[0053] By applying overdrive in a progressive manner (e.g., as
shown in FIGS. 4A and 4B), the overdrive circuitry 240 may ensure
that each of the pixel elements in the array 210 is updated to its
target pixel value (or at least a pixel value that is substantially
close to the target pixel value) before the next display period.
Furthermore, by selectively applying overdrive to only a portion of
the pixel array (e.g., as shown in FIG. 4B), the embodiments herein
may reduce the amount of resources (e.g., memory, time, power, and
other processing resources) needed to generate the overdrive
voltages for the pixel array 210.
[0054] FIG. 5A shows a block diagram of a progressive overdrive
controller 500A, in accordance with some embodiments. The
progressive overdrive controller 500A may be an example embodiment
of the overdrive circuitry 240 of FIG. 2. Thus, the progressive
overdrive controller 500A may be configured to progressively
increase the amount of overdrive applied to one or more rows of
pixel elements of a pixel array (such as the pixel array 210 of
FIG. 2) based, at least in part, on the row position in the array
210.
[0055] The progressive overdrive controller 500A includes an
overdrive voltage generator 510, a previous image buffer 520, and a
lookup table (LUT) repository 530. The overdrive voltage generator
510 may determine an overdrive pixel voltage 505 to be applied to
each pixel element of the associated pixel array. More
specifically, the overdrive voltage generator 510 may generate the
overdrive pixel voltage 505 based, at least in part, on a target
pixel value 501, a current pixel value 502, and an overdrive (OD)
index 503. The target pixel value 501 may correspond to the pixel
value that a particular pixel element is to be driven by the next
display period. For example, the target pixel value 501 may be
provided by an input image buffer (such as the display memory 230
of FIG. 2). The current pixel value 502 may correspond to the pixel
value, for the particular pixel element, that was displayed during
the previous display period. For example, the current pixel value
502 may be stored in, and retrieved from, the previous image buffer
520. In some aspects, after each frame update, the overdrive
voltage generator 510 may store the target pixel value 501 of the
current frame in the previous image buffer 520 (e.g., to be used as
the current pixel value 502 for the next frame update).
[0056] In some embodiments, the overdrive voltage generator 510 may
determine the overdrive pixel voltage 505 by comparing the target
pixel value 501 with the current pixel value 502. More
specifically, the progressive overdrive controller 510 may
determine an amount of voltage to be applied to a corresponding
pixel element to change the pixel value from the current pixel
value 502 to the target pixel value 501. In some aspects, the
overdrive voltage generator 510 may compare the target pixel value
501 and the current pixel value 502 to corresponding values in a
lookup table (LUT) to determine the overdrive pixel voltage 505.
For example, the rows of the LUT may correspond with a plurality of
current pixel values and the columns of the LUT may correspond with
a plurality of target pixel values. The intersection of a
particular row and a particular column may indicate the overdrive
voltage needed to change the pixel value from the current pixel
value (of the corresponding row) to the target pixel value (of the
corresponding column).
[0057] Conventional LCD displays use a single lookup table to
determine the overdrive voltage to be applied to any pixel element
in the pixel array. However, in HMD devices (and particularly for
VR applications), different pixel elements may have different
timing constraints (e.g., to reach a target brightness or pixel
value) based on their position in the array (e.g., as described
with respect to FIG. 3). For example, pixel elements in the first
row of the array may have significantly more time to reach their
target pixel values than pixel elements in the last row of the
array. Thus, the progressive overdrive controller 500A may
progressively increase (or decrease) the amount of overdrive
voltage, to effect a given change in pixel value, for a plurality
of successive rows of pixel elements in the pixel array (e.g., as
described with respect to FIGS. 4A and 4B).
[0058] In some embodiments, the overdrive voltage generator 510 may
use a plurality of LUTs to determine the overdrive pixel voltage
505. For example, the LUT repository 530 may store a plurality of
LUTs that may be retrieved by the overdrive voltage generator 510.
Each of the plurality of LUTs may be associated with a different
row of pixel elements in the corresponding pixel array. For
example, the LUT repository 530 may store a first LUT associated
with the first row of the pixel array and a second LUT associated
with the last row of the pixel array. The first LUT may indicate a
plurality of overdrive voltages to be used to implement various
changes in pixel values for any pixel element in the first row of
the array, whereas the second LUT may indicate a plurality of
overdrive voltages to be used to implement various changes in pixel
values for any pixel element in the last row of the array. Since
pixel elements in the last row of the array may have less time to
reach their target pixel values than pixel elements in the first
row of the array, the overdrive voltages in the second LUT may be
greater than corresponding overdrive voltages in the first LUT.
[0059] In some embodiments, the overdrive voltage generator 510 may
use the overdrive index 503 to determine the overdrive voltages for
a particular row of pixel elements. More specifically, the
overdrive index 503 may be used to select one or more LUTs from the
LUT repository 530. For example, in some aspects, the overdrive
index 503 may be based, at least in part, on the line or row number
associated with the pixel elements to be driven. However, other
factors may also affect the amount of overdrive voltage needed to
achieve a desired change in pixel value within a frame update
period. For example, the responsiveness of the liquid crystals may
vary with respect to the temperature of the display. Warmer pixel
elements tend to exhibit faster response times, and thus require
less overdrive voltage to achieve the same change in pixel value,
than colder pixel elements. Thus, for any given row of pixel
elements, the overdrive voltage generator 510 may use a different
LUT to determine the overdrive voltages under warmer temperature
conditions than under colder temperature conditions. In some
embodiments, the overdrive index 503 may be based on a combination
of factors including, but not limited to, the line or row number
associated with the pixel elements to be driven and the temperature
of the display.
[0060] For example, FIG. 5B shows a progressive overdrive
controller 500B that may dynamically adjust the overdrive pixel
voltages 505 based on the temperature of the LCD display. In
addition to the overdrive voltage generator 510, the previous image
buffer 520, and the LUT repository 530 (described above with
respect to FIG. 5A), the progressive overdrive controller 500B also
includes a temperature sensor 540 that may provide temperature
readings 506 to a processor (e.g., CPU) 550 external to the
progressive overdrive controller 500B and/or the display driver.
For example, the CPU 550 may reside on a host device (or elsewhere
on the display device) that has greater memory and processing
resources than the display driver. Because the temperature sensor
540 resides on the display device (e.g., proximate to the LCD
display), the temperature readings 506 may provide a relatively
accurate indication of the temperature of the LCD display.
[0061] In some embodiments, the CPU 550 may use the temperature
readings 506 to select a set of temperature-specific LUTs 507 from
an external LUT repository 560. As described above, the
responsiveness of the liquid crystals in an LCD display may vary
with respect to the temperature of the LCD display. Thus, for any
given row of pixel elements, it may be desirable to use a different
LUT to determine the overdrive voltages under warmer temperature
conditions than under colder temperature conditions. However,
aspects of the present disclosure recognize that the memory
resources of the display driver may be very scarce. As a result,
the LUT repository 530 may be able to store only a limited number
of LUTs at any given time. Thus, in some embodiments, the CPU 550
may dynamically update and/or populate the LUT repository 530 with
temperature-specific LUTs 507 retrieved from the external LUT
repository 560 based on the current temperature of the LCD display
(e.g., as indicated by the temperature readings 506).
[0062] In some embodiments, the LUT repository 530 may store a
different LUT for each row of the pixel array. For example, the
overdrive index 503 may specify the precise LUT 504 to be retrieved
by the overdrive voltage generator 510 for a particular row of
pixel elements. However, aspects of the present disclosure
recognize that it may not be practical, or even feasible, to store
that many LUTs (e.g., since an LCD display may contain hundreds, if
not thousands, of rows of pixel elements). Thus, in other
embodiments, the LUT repository 530 may store LUTs for only a
subset of rows of the pixel array. Accordingly, the overdrive
voltage generator 510 may determine the overdrive pixel voltage 505
for a particular pixel element based on a bilinear interpolation of
multiple LUTs. For example, the overdrive voltage generator 510 may
retrieve the two LUTs 504, from the LUT repository, that are
closest to the overdrive index 503. The overdrive voltage generator
510 may then perform bilinear interpolation on the two LUTs 504 to
determine the overdrive pixel voltage 505 to be applied to each
pixel element in the selected row in order to change the
corresponding pixel value from the current pixel value 502 to the
target pixel value 501.
[0063] FIG. 6 shows an example pair of look-up tables (LUTs) 601
and 602 that can be used to generate progressive overdrive
voltages, in accordance with some embodiments. In the example of
FIG. 6, each of the LUTs 601 and 602 may be a 17.times.17 LUT. Each
element (e.g., cell) of the LUTs may store an 8-bit grayscale pixel
value. Each of the LUTs 601 and 602 may be associated with a
different row of pixel elements in a corresponding pixel array.
[0064] In a particular example, with reference to FIG. 4B, the
first LUT 601 may be associated with the row of pixel elements at
line number l.sub.n and the second LUT 602 may be associated with
the row of pixel elements at line number l.sub.p. Thus, the first
LUT 601 may include a plurality of overdrive voltages (e.g.,
v.sub.a1-v.sub.a20) that can be used to drive a pixel element
coupled to line number l.sub.n from a current pixel value (e.g.,
indexed along the rows of the LUT 601) to a target pixel value
(e.g., indexed along the columns of the LUT 601). Similarly, the
second LUT 602 may include a plurality of overdrive voltages (e.g.,
v.sub.b1-v.sub.b20) that can be used to drive a pixel element
coupled to line number l.sub.p from a current pixel value (e.g.,
indexed along the rows of the LUT 602) to a target pixel value
(e.g., indexed along the columns of the LUT 602). Because the pixel
elements coupled to line number l.sub.n may have more time to reach
their target pixel values than the pixel elements coupled to line
number l.sub.p, each of the overdrive voltages in the second LUT
602 may be greater than corresponding overdrive voltages in the
first LUT 601 (e.g., V.sub.b1>V.sub.a1, V.sub.b2>V.sub.a2,
V.sub.b3>V.sub.a3, etc.)
[0065] In some embodiments, the LUTs 601 and 602 may be used to
derive overdrive voltages for pixel elements in any row of the
array between line numbers l.sub.n and l.sub.p (e.g., based on a
bilinear interpolation of the LUTs 601 and 602). In some aspects,
the LUTs 601 and 602 may be combined, through linear interpolation,
to produce a new LUT 603 for a selected row of pixel elements
between lines numbers l.sub.n and l.sub.p. Thus, each element of
the new LUT 603 may be generated based on a linear interpolation of
corresponding elements in the first and second LUTs 601 and 602, as
represented by the equation below:
overdrive_voltage=L.sub.i(v.sub.ax,v.sub.bx)
where i is the overdrive index for the selected row of pixel
elements, and x may be any integer value from 1 to 272. Thus,
depending on the overdrive index, the linear interpolation of the
overdrive voltages from LUT 601 and LUT 602 may result in a
plurality of voltages that are closer to those of the first LUT 601
(e.g., if the selected row of pixel elements is closer to line
l.sub.n) or closer to those of the second LUT 602 (e.g., if the
selected row of pixel elements is closer to line l.sub.p).
[0066] Each cell of the new LUT 603 may represent a respective
overdrive voltage that can be used to drive a pixel element in the
selected row from a current pixel value (e.g., indexed along the
rows of the LUT 603) to a target pixel value (e.g., indexed along
the columns of the LUT 603). It is noted that the new LUT 603 (as
well is the other LUTs 601 and 602) may include only a subset of
the total possible grayscale values (e.g., 0, 16, 32, 48, 64, 80,
96, 112, 128, 144, 160, 176, 192, 208, 224, 240, and 255). Thus, an
additional step of interpolation may be used to determine the
overdrive voltages associated with any grayscale values that fall
between the grayscale values explicitly identified in the LUT 603.
For example, the overdrive voltage to be used to drive a pixel
element from a grayscale value of 8 to a grayscale value of 20 may
be determined based on a bilinear interpolation of the current
grayscale values 0 and 16 and the target grayscale values 16 and
32.
[0067] FIG. 7 shows a block diagram of a progressive overdrive
controller 700, in accordance with some other embodiments. The
progressive overdrive controller 700 may be an example embodiment
of the progressive overdrive controller 500A of FIG. 5A and/or the
overdrive circuitry 240 of FIG. 2. Thus, the progressive overdrive
controller 700 may be configured to progressively increase the
amount of overdrive applied to one or more rows of pixel elements
of a pixel array (such as the pixel array 210 of FIG. 2) based, at
least in part, on the row position in the array 210.
[0068] The progressive overdrive controller 700 includes an
overdrive voltage interpolator 710, a previous image buffer 720, a
lookup table (LUT) repository 730, a lookup table (LUT) generator
740, and a lookup table (LUT) buffer 750. The overdrive voltage
interpolator 710 may determine an overdrive pixel voltage 704 to be
applied to each pixel element of the associated pixel array. More
specifically, the overdrive voltage interpolator 710 may generate
the overdrive pixel voltage 704 based, at least in part, on a
target pixel value 701, a current pixel value 702, and a lookup
table (LUT). The target pixel value 701 may correspond to the pixel
value that a particular pixel element is to be driven by the next
display period. For example, the target pixel value 701 may be
provided by an input image buffer (such as the display memory 230
of FIG. 2). The current pixel value 702 may correspond to the pixel
value, for the particular pixel element, that was displayed during
the previous display period. For example, the current pixel value
702 may be stored in, and retrieved from, the previous image buffer
720. In some aspects, after each frame update, the overdrive
voltage interpolator 710 may store the target pixel value 701 of
the current frame in the previous image buffer 720 (e.g., to be
used as the current pixel value 702 for the next frame update).
[0069] In some embodiments, the overdrive voltage interpolator 710
may determine the overdrive pixel voltage 704 by comparing the
target pixel value 701 with the current pixel value 702. More
specifically, the overdrive voltage interpolator 710 may determine
an amount of voltage to be applied to a corresponding pixel element
to change the pixel value from the current pixel value 702 to the
target pixel value 701. In some aspects, the overdrive voltage
interpolator 710 may compare the target pixel value 701 and the
current pixel value 702 to corresponding values in a LUT to
determine the overdrive pixel voltage 704. In some embodiments, the
progressive overdrive controller 700 may progressively increase (or
decrease) the amount of overdrive voltage, for a given change in
pixel value, for a plurality of successive rows of pixel elements
in the pixel array. Thus, in some aspects, the overdrive voltage
interpolator 710 may use different (or updated) LUTs to determine
the overdrive pixel voltages 704 for different rows of the pixel
array.
[0070] In some embodiments, the LUT repository 730 may store a
plurality of LUTs associated with different rows of the pixel
array. More specifically, the LUT repository 730 may store LUTs for
only a subset of rows of the pixel array. In some aspects, the LUT
repository 730 may store at least 2, and up to 5, LUTs for a given
pixel array. At least one of the LUTs may be associated with a
minimum overdrive voltage to be applied to one or more rows of
pixel elements in the array (e.g., pixel elements coupled to line
number l.sub.0 of FIG. 4A or line numbers l.sub.0-l.sub.n of FIG.
4B), and at least one of the LUTs may be associated with a maximum
overdrive voltage to be applied to one or more rows of pixel
elements in the array (e.g., pixel elements coupled to line numbers
l.sub.p-l.sub.M in FIGS. 4A and 4B).
[0071] The LUT generator 740 may retrieve one or more LUTs (LUT+
and LUT-) from the LUT repository 730 based, at least in part, on
an overdrive index 703. In some aspects, the overdrive index 703
may be based, at least in part, on the line or row number
associated with the pixel elements to be drive. In some other
aspects, the overdrive index 703 may be based on a combination of
factors including, but not limited to, the line or row number
associated with the pixel elements to be driven and the temperature
of the display. In some embodiments, the LUT generator 740 may
retrieve a pair of LUTs that are closest to the overdrive index
703. For example, if the overdrive index 703 corresponds to a
particular LUT stored in the LUT repository 730, the LUT generator
740 may retrieve two copies of the same LUT. However, if the
overdrive index 703 does not correspond to any particular LUT
stored in the LUT repository, the LUT generator 740 may retrieve
the closest LUT having an index above the overdrive index 703
(e.g., LUT+) associated with the overdrive index 703 and the
closest LUT having an index below the overdrive index 703 (e.g.,
LUT-).
[0072] The LUT generator 740 may interpolate the LUTs retrieved
from the LUT repository 730 to generate an interpolated LUT
(Int_LUT). In some embodiments, the interpolated LUT may be based,
at least in part, on a linear interpolation of the LUTs retrieved
from the LUT repository 730 (e.g., as described above with respect
to FIG. 6). More specifically, each element of the interpolated LUT
may be generated based on a linear interpolation of corresponding
elements in LUT+ and LUT-. Thus, depending on the overdrive index
703, the overdrive voltages in the interpolated LUT may be closer
to the voltages of LUT+ (e.g., if the overdrive index 703 is closer
to that of LUT+) or closer to the voltages of LUT- (e.g., if the
overdrive index 703 is closer to that of LUT-). Each cell of the
interpolated LUT may represent a respective overdrive voltage that
can be used to drive a pixel element in a selected row of the pixel
array (e.g., associated with the overdrive index 703) from a
current pixel value to a target pixel value.
[0073] The interpolated LUT may be stored in the LUT buffer 750 and
accessed by the overdrive voltage interpolator 710. For example,
the overdrive voltage interpolator 710 may look up the target pixel
value 701 and the current pixel value 702 in the interpolated LUT
to determine the overdrive pixel voltage 704. In some embodiments,
the interpolated LUT may include only a subset of the total
possible grayscale values for each of the target pixel values and
current pixel values. Thus, in some aspects, the overdrive voltage
interpolator 710 may interpolate the pixel values in the
interpolated LUT to generate the overdrive pixel voltage 704. For
example, the overdrive voltage interpolator 710 may retrieve the
row of overdrive voltages associated with the closest current pixel
value (in Int_LUT) above the current pixel value 702 (e.g.,
V.sub.CP+), the row of overdrive voltages associated with the
closest current pixel value (in Int_LUT) below the current pixel
value 702 (e.g., V.sub.CP-), the column of overdrive voltages
associated with the closest target pixel value (in Int_LUT) above
the target pixel value 701 (e.g., V.sub.TP+), and the column of
overdrive voltages associated with the closest target pixel value
(in Int_LUT) below the target pixel value 701 (e.g., V.sub.TP-).
The overdrive voltage interpolator 710 may then generate the
overdrive pixel voltage 704 based on a bilinear interpolation of
V.sub.CP+, V.sub.CP-, V.sub.TP+, and V.sub.TP-.
[0074] It is noted that, when implementing progressive overdrive,
the overdrive voltage interpolator 710 may use a different (or
updated) interpolated LUT for each successive row of pixel elements
in the array. Thus, in some embodiments, interpolated LUTs from the
LUT generator 740 may be double-buffered by the LUT buffer 750. For
example, the LUT buffer 750 may store the interpolated LUT for the
current row of pixel elements as well as the interpolated LUT for
the next row of pixel elements to be processed by the overdrive
voltage interpolator 710. This allows the overdrive voltage
interpolator 710 to derive the overdrive pixel voltages 704 for the
next row of pixel elements immediately after processing the
overdrive pixel voltages 704 for the current row of pixel elements
(e.g., without waiting for the next interpolated LUT to be
buffered).
[0075] In conventional display systems, LCD overdrive circuitry
(such as the overdrive circuitry 240 of FIG. 2) is provided on (or
implemented by) a display driver residing on the display device
(e.g., display device 120). Thus, the display driver may generate
the overdrive voltages to be applied to each pixel element while
concurrently rendering each frame of display data received from the
host. However, because several LUTs are used to implement
progressive overdrive, the display device may require a substantial
amount of memory and other hardware resources to store and process
each LUT for the various rows of pixel elements. Since resources
are much more limited on a display device than a host device, it
may be desirable to perform some (or all) of the progressive
overdrive processing on the host device.
[0076] In some embodiments, the overdrive voltages for each pixel
element in the pixel array may be generated or determined by the
host device. With reference for example to FIG. 1, the host device
110 may generate the overdrive voltages concurrently while
processing the image source data 101 for display on the display
device 120. Accordingly, the host device 110 may send the overdrive
voltage information, together with the display data 102, to the
display device 120. In some embodiments, the host device 110 may
record the overdrive voltage information in the display data 102.
Thus, upon receiving the display data 102 from the host device 110,
the display device 120 may render the corresponding image on the
display 122 using the correct overdrive voltages for each row of
pixel elements in that particular frame.
[0077] FIG. 8 is an illustrative flowchart depicting an example
operation 800 for driving a pixel element of a display to a target
pixel value. With reference for example to FIGS. 1 and 2, the
example operation 800 may be performed by any display device of the
present disclosure (e.g., display device 120 or display device
200).
[0078] The display device determines a current pixel value for a
first pixel element of a pixel array (810). For example, the
current pixel value may correspond to a color and/or intensity of
the first pixel element as currently on display (e.g., for the
current frame or image). The first pixel element may comprise a
plurality of subpixels including, but not limited to, red (R),
green (G), and blue (B) subpixels. In some aspects, the current
pixel value may correspond to R, G, and B values for the subpixels
of the first pixel element. The R, G, and B values may affect the
color and intensity (e.g., gray level) of the first pixel element.
For example, each pixel value may be an 8-bit value representing
one of 256 possible grayscale levels.
[0079] The display device further determines a target pixel value
for the first pixel element (820). For example, the target pixel
value may correspond to a desired color and/or intensity of the
first pixel element to be displayed (e.g., for the next frame or
image in a sequence). The target pixel value may be achieved by
applying voltage to the first pixel element. More specifically, the
voltage may change the physical state (e.g., rotation) of the first
pixel element, resulting in a corresponding change in color and/or
intensity. In some aspects, the target pixel value may be
associated with a target voltage which, when applied to the first
pixel element, causes the first pixel element to settle at the
target pixel value.
[0080] The display device may determine a first voltage to be
applied to the first pixel element based at least in part on a
position of the first pixel element in the pixel array (830). More
specifically, the first voltage may cause the first pixel element
to transition from the current pixel value to the target pixel
value by a first instance of time (e.g., the start of a display
period). However, aspects of the present disclosure recognize that,
because a pixel array is updated on a row-by-row basis, different
pixel elements may have different transition times depending on
their row positions in the pixel array. For example, pixel elements
associated with higher line numbers (e.g., pixel elements that are
updated later) may have less time to transition to their desired
pixel values than pixel elements associated with lower line numbers
(e.g., pixel elements that are updated earlier). Accordingly, the
row position of the first pixel element may affect the amount of
time the first pixel element has to transition from the current
pixel value to the target pixel value as well as the voltage to be
applied to cause the transition within the allotted time.
[0081] The display device may apply the first voltage to the first
pixel element before the first instance of time (840) and activate
one or more light sources to illuminate the pixel array at the
first instance of time (850). For example, the first pixel element
may begin to transition towards the target pixel value once the
first voltage is applied. However, the first pixel element may or
may not settle at the target pixel value by the start of the
display period depending on its row position. For example, when
driven to the target voltage, the first pixel element may settle at
the target pixel value by the start of the display period. When
driven to an overdrive voltage, the first pixel element may reach
the target pixel value at the start of the display period but may
continue to transition even after the display period (e.g.,
eventually settling at a higher or lower pixel value than the
target pixel value). However, because the pixel elements are
illuminated only during the display periods, any changes in pixel
value exhibited before or after the display period will not be seen
by the user.
[0082] FIG. 9 is an illustrative flowchart depicting an example
operation 900 for selectively applying overdrive voltages to the
pixel elements of a pixel array. With reference for example to
FIGS. 2, 5A, 5B, and 7 the example operation 900 may be performed
by the overdrive circuitry 240 and/or the progressive overdrive
controller 500A, 500B, and/or 700. In some embodiments, the example
operation 900 may be used to determine the voltage to be applied to
a particular pixel element to cause the pixel element to transition
from a current pixel value to a target pixel value.
[0083] The overdrive circuitry may first determine a row position
of a selected pixel element (910). For example, the row position
may correspond to a particular line number of the corresponding
pixel array. In some aspects, the row position may indicate an
order in which the selected pixel element is updated in the pixel
array. For example, individual rows of the pixel array may be
successively updated (e.g., one row at a time), from the lowest
line number (l.sub.0) to the highest line number (l.sub.M).
[0084] The overdrive circuitry may compare the row position of the
selected pixel element to a first threshold line number limn (920).
For example, the first threshold line number (e.g., line l.sub.n of
FIG. 4B) may correspond to a row of the pixel array at which
overdrive is first applied. Aspects of the present disclosure
recognize that, because a pixel array is updated on a row-by-row
basis, different pixel elements may have different transition times
depending on their row positions in the pixel array. More
specifically, pixel elements having a row position lower than the
first threshold line number (e.g., between lines l.sub.0 and
l.sub.n) may have sufficient time to settle at their target pixel
values before the next display period.
[0085] Thus, when the row position of the selected pixel element is
lower than the first threshold line number (as tested at 920), the
overdrive circuitry may select the target voltage to be applied to
the selected pixel element (930). As described above, the target
voltage may be a voltage which, when applied to the selected pixel
element, causes the selected pixel element to settle at the target
pixel value.
[0086] However, when the row position of the selected pixel element
is not lower than the first threshold line number (as tested at
920), the overdrive circuitry may further compare the row position
of the selected pixel element to a second threshold line number
l.sub.TH2 (940). For example, the second threshold line number
(e.g., line l.sub.p of FIGS. 4A and 4B) may correspond to a row of
the pixel array at which maximum overdrive is first applied.
Aspects of the present disclosure recognize that the amount of
voltage that can be applied to a pixel element may be limited by
the voltage range of the pixel element (or data driver).
Accordingly, the overdrive voltage may become saturated by the time
pixel elements having a row position higher than the second
threshold line number (e.g., above line l.sub.p) are updated.
[0087] Thus, when the row position of the selected pixel element is
higher than the second threshold line number (as tested at 940),
the overdrive circuitry generator may select a maximum overdrive
voltage to be applied to the selected pixel element (950). As
described above, the maximum overdrive voltage may be the highest
(or lowest) achievable voltage in the voltage range of the pixel
element (or data driver).
[0088] However, when the row position of the selected pixel element
falls between the first threshold line number (as tested at 930)
and the second threshold line number (as tested at 940), the
overdrive circuitry may apply a progressive overdrive to the
selected pixel element (960). As described above with respect to
FIGS. 4A and 4B, the amount of overdrive may be progressively
increased for each successive row of pixel elements from lines
l.sub.n to l.sub.p. For example, a pixel element coupled to line
l.sub.p may be driven to a higher voltage than a pixel element
coupled to line l.sub.n to produce the same change in pixel value.
In some embodiments, the overdrive circuitry may determine the
amount of overdrive voltage to be applied to the selected pixel
element based at least in part on one or more lookup tables (LUTs)
stored in an LUT repository.
[0089] FIG. 10 is an illustrative flowchart depicting an example
operation 1000 for determining an overdrive voltage to be used to
drive a pixel element to a target pixel value. With reference for
example to FIGS. 2, 5A, 5B, and 7 the example operation 1000 may be
performed by the overdrive circuitry 240 and/or the progressive
overdrive controller 500A, 500B, and/or 700. In some embodiments,
the example operation 1000 may be used to determine the voltage to
be applied to a particular pixel element to cause the pixel element
to transition from a current pixel value to a target pixel
value.
[0090] The overdrive circuitry may first receive an overdrive index
(1010). In some aspects, the overdrive index 503 may be based, at
least in part, on the line or row number associated with the pixel
element(s) to be driven. However, other factors may also affect the
amount of overdrive voltage needed to achieve a desired change in
pixel value within a frame update period. For example, the
responsiveness of the liquid crystals may vary with respect to the
temperature of the display. Thus, in some embodiments, the
overdrive index 503 may be based on a combination of factors
including, but not limited to, the line or row number associated
with the pixel elements to be driven and the temperature of the
display.
[0091] The overdrive circuitry may select a first lookup table
(LUT) based on the overdrive index (1020). For example, the
overdrive circuitry may include a LUT repository that stores a
plurality of LUTs. More specifically, each of the LUTs may indicate
a plurality of overdrive voltages for pixel elements in a
corresponding row of the pixel array (as described above with
respect to FIG. 6). In some embodiments, the LUT repository may
store a different LUT for each row of the pixel array. In some
other embodiments, the LUT repository may store LUTs for some, but
not all, of the rows of the pixel array. The first LUT selected by
the overdrive circuitry may correspond to an LUT associated with
the nearest row equal to or below the row position or line number
indicated by the overdrive index.
[0092] The overdrive circuitry may further select a second LUT
based on the overdrive index (1030). The second LUT selected by the
overdrive circuitry may correspond to an LUT associated with the
nearest row equal to or above the row position or line number
indicated by the overdrive index. As described above, in some
embodiments, the LUT repository may store a different LUT for each
row of the pixel array. In such implementations, there may be an
exact LUT associated with the row position indicated by the
overdrive index. Thus, in some aspects, the second LUT may be the
same as the first LUT (e.g., the nearest LUT equal to or above the
overdrive index is the same as the nearest LUT equal to or below
the overdrive index).
[0093] The overdrive circuitry may generate an interpolated LUT
based on a linear interpolation of the first and second LUTs
(1040). For example, each element of the interpolated LUT may be
generated based on a linear interpolation of corresponding elements
in the first LUT and the second LUT (e.g., as described above with
respect to FIG. 6). Thus, depending on the overdrive index, the
overdrive voltages in the interpolated LUT may be closer to the
voltages of the first LUT (e.g., if the overdrive index is closer
to the row associated with the first LUT) or closer to the voltages
of the second LUT (e.g., if the overdrive index is closer to the
row associated with the second LUT).
[0094] Finally, the overdrive circuitry may determine overdrive
voltages to be applied to the row of pixel elements associated with
the overdrive index based on a bilinear interpolation of the rows
and columns of the interpolated LUT (1050). For example, each cell
of the interpolated LUT may represent a respective overdrive
voltage that can be used to drive a pixel element in a selected row
of the pixel array from a current pixel value to a target pixel
value (e.g., as described above with respect to FIG. 6). However,
in some embodiments, the interpolated LUT may include only a subset
of the total possible grayscale values for each of the target pixel
values and current pixel values. Thus, in some aspects, the
overdrive circuitry may interpolate the pixel values in the
interpolated LUT to determine the overdrive voltage to effect a
transition from any current pixel value to any target pixel value
(e.g., as described above with respect to FIG. 6).
[0095] Those of skill in the art will appreciate that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0096] Further, those of skill in the art will appreciate that the
various illustrative logical blocks, modules, circuits, and
algorithm steps described in connection with the aspects disclosed
herein may be implemented as electronic hardware, computer
software, or combinations of both. To clearly illustrate this
interchangeability of hardware and software, various illustrative
components, blocks, modules, circuits, and steps have been
described above generally in terms of their functionality. Whether
such functionality is implemented as hardware or software depends
upon the particular application and design constraints imposed on
the overall system. Skilled artisans may implement the described
functionality in varying ways for each particular application, but
such implementation decisions should not be interpreted as causing
a departure from the scope of the disclosure.
[0097] The methods, sequences or algorithms described in connection
with the aspects disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module may reside in RAM memory,
flash memory, ROM memory, EPROM memory, EEPROM memory, registers,
hard disk, a removable disk, a CD-ROM, or any other form of storage
medium known in the art. An exemplary storage medium is coupled to
the processor such that the processor can read information from,
and write information to, the storage medium. In the alternative,
the storage medium may be integral to the processor.
[0098] In the foregoing specification, embodiments have been
described with reference to specific examples thereof. It will,
however, be evident that various modifications and changes may be
made thereto without departing from the broader scope of the
disclosure as set forth in the appended claims. The specification
and drawings are, accordingly, to be regarded in an illustrative
sense rather than a restrictive sense.
* * * * *